Stem cells taken from muscle tissue can be used to build new blood
vessels for transplants, researchers reported on Friday.

They grew these stem cells on elastic biodegradable tubes to engineer
new blood vessels for rats within days of extracting the cells.

The finding, presented at a meeting in Toronto, might lead to a
way to create customized blood vessel grafts to use in patients
with heart and kidney disease, the researchers said.

These so-called muscle-derived stem cells are adult stem cells
-- distinct from the embryonic versions that are currently under
debate.

The researchers sprayed, or seeded, 10 million of these stem cells
into tubes just 0.05 inch (1.2 mm) in diameter.

The stem cells grew on these scaffolds for a week before the tubes
were sewn into the major artery in each rat's abdomen.

Eight weeks later, they found that the graft, guided by cues such
as blood pressure from the surrounding tissue, had remodeled itself
to resemble a mature artery. They had layers of distinct cells,
including the endothelial calls that line natural blood vessels.

In theory, these stem cells can regenerate entire blood vessels,
but the researchers are still trying to figure out how much the
cells actually contribute, said David Vorp at the University of
Pittsburgh School of Medicine, who led the study.

They did find, however, that the technique seemed to prevent the
often deadly blood clots that can appear in other grafts.

As it degrades over the course of months, the tube "gives
the space for cells to grow and regenerate to extend systemic circulation,"
said Alejandro Nieponice, who also worked on the study.

Other researchers are experimenting with similar approaches by
taking stem cells from bone marrow or harvested blood vessels, he
said.

They usually take an artery or a vein from a patient's leg for
procedures such as coronary artery bypass grafts, but these require
extra surgery and are prone to clots. Blood clots are also an issue
in other synthetic grafts, which are often stiffer than natural
blood vessels, Nieponice said.

The researchers hope to eventually use this technique on humans
by extracting muscle stem cells from a tiny plug in a patient's
thigh, then culturing and implanting them in the patient within
days or even immediately, said Vorp.

In the meantime, his team will try to make the procedure work in
pigs, which have blood that more closely resembles that of humans.

About 1 million vascular bypass grafts are performed each year
in the United States, according to Nieponice.